Genesis of the Moly Brook molybdenum-copper deposit, Newfoundland, Canada: Geological and geochemical constraints on fluid evolution, links with adjacent tungsten mineralization, and the role of Late Devonian granitic intrusions

• Main Author: Lynch, Edward P.
• Other Authors: Feely, Martin, Selby, David, Wilton, Derek H. C., Murray, John, Ireland Newfoundland Partnership, Society of Economic Geologists Foundation, School of Natural Sciences, NUIG, Irish Research Council for Science, Engineering and Technology
• Format: Thesis
• Language: unknown
• Published: NUI Galway 2017
• Subjects: Moly Brook; Newfoundland; Molybdenum; Re-Os geochronology; Hydrothermal fluids; Granite; Appalachians; Natural Sciences; Earth and Ocean Science; Canada; Wall Rocks
• Online Access: http://hdl.handle.net/10379/7323; https://doi.org/10.13025/17346

An integrated geological, structural and geochemical study of the Moly Brook Mo-Cu deposit, southern Newfoundland (Canada), is presented. The role of subordinate leucogranite as progenitor to the mineralizing components (e.g. fluids, metals, sulfur) is assessed. Re-Os molybdenite dating constrains the timing of Mo-Cu-(W) mineralization and establishes a temporal framework for Late Devonian granite-hydrothermal systems in this sector of the northern Appalachian orogen. The Moly Brook deposit comprises a c. 0.8 x 1 km, c. N- to NNE-trending vein network that transects the c. 412 Ma Burgeo Intrusive Suite [BIS]. At the deposit, BIS wall rocks are moderately to intensely deformed and contain structures consistent with cataclasis within an c. E-W-trending deformation zone. Four wall rock subunits (megacrystic, intermediate, mafic, granitic) reflect igneous heterogeneities and variable responses to episodic deformation-metasomatism and alteration. Compared to distal (less altered) equivalents, BIS wall rocks display geochemical characteristics reflecting episodic modification by early pervasive calcic ± sodic metasomatism and subsequent vein-related potassic ± phyllic alteration associated with Mo-Cu mineralization. Overall, the vein network has a sheeted conjugate form, with local stockwork or irregular zones also occurring. Individual veins mainly strike c. NNW – NNE and are steeply c. E- or W-dipping. Subordinate c. E-W-striking veins also occur and exploit older structural fabrics. Vein characteristics, geometries and growth textures (e.g. crustiform banding) indicate the network formed under dominantly extensional conditions during a single phase of multi-step (cyclical) hydrofracturing. During veining, the maximum effective principal stress (σ’1) had a sub-vertical orientation, while fluctuating fluid pressures produced variable effective differential stress (σ’3 ≥ σ’2) which influenced vein orientations and formation modes. Paragenetically early, nonplanar, sulfide-bearing veins also suggest mineralization ...